A reduction in recent years in the number of cases of breast cancer in women aged 50-59 years most probably depends on a decrease in the use of hormone replacement therapy to relieve problems associated with the menopause. A large Swedish study under the auspices of Karolinska Institutet confirms suspicions against the hormone therapy.
The use of hormone replacement therapy (HRT) to relieve problems associated with the menopause reached a peak in Sweden in 1999 and then began to fall. The fall was accentuated after a large investigation in 2002 called the treatment into question. Several studies have shown that the number of cases of breast cancer fell suddenly in several countries, but it has not been clear whether the reduction in the use of HRT was the principal cause.
Swedish scientists have now investigated trends in the incidence of breast cancer in Sweden between 1997 and 2007, a period during which the use of HRT fell dramatically. The percentage of women aged 50-59 years who used HRT fell from a peak of 36% in 1999 to 27% in 2002, and to 9% in 2007.
Our results provide further support for the hypothesis that the decreased use of HRT to relieve problems associated with the menopause has reduced the incidence of breast cancer in recent years, for women aged 50-59 years. The reduction we have seen cannot be explained by changes in the procedures used to record cases of breast cancer or by a reduction in the use of mammography, says Mats Lambe, author of the study and working at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet.
The type of cancer known as carcinoma in situ is most often detected by mammography. If the use of mammography had fallen during the period of the study, the reported incidence of carcinoma in situ should also have fallen. Mats Lambes study, published in the scientific journal Breast Cancer Research and Treatment shows, however, that this was not the case. Scientists at other centres, including Uppsala University and the Sahlgrenska Academy, have participated in the work.
Mats Lambe, Annette Wigertz, Marit Holmqvist, Jan Adolfsson, Carola Bardage, Tommy Fornander, Per Karlsson, Viveca Odlind, Ingemar Persson, Johan Ahlgren & Leif BergkvistReductions in use of hormone replacement therapy: effects on Swedish breast cancer incidence trends only seen after several years
Breast Cancer Res Treat, Epub ahead of print 6 November 2009, DOI 10.1007/s10549-009-0615-7